Reflection from a surface

The eye detects intensity changes rather than amplitude changes, and so it is more convenient to work with the reflectivity or reflectance, R  

This is because the intensity, /o, is proportional to the square of the amplitude, (ao). The reflected intensity, R(Io), is proportional to r aof. The reflectivity, R, for a plate of a transparent material of refractive index in air is  

As n depends on wavelength, the reflectivity will vary across the spectrum. When the reflecting surface is a metal, it is necessary to use the complex refractive index, N = N + ik. In this case, the reflectivity of a metallic surface at normal incidence is 

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Ellipsometry measurement of the characteristics of polarised light after reflection from a surface. 

Albedo The amount of radiation reflected from a surface across all wavelengths. 

Spectroscopic Ellipsometry Porosimetry (EP). In general, ellip-sometry takes advantage of the change of polarization of a polarized light beam after reflection from a surface. From the parameters (T and A), obtained... 

Wasserman [186] has described the use of both low-angle X-ray reflectivity and ellipsometry for the determination of thickness of Cio-Cig SAMs prepared on surface silanol groups of silicon plates. Ellipsometry is based on the reflection of polarized light from a sample and depends on the sample s thickness and refractive index. X-ray reflectivity measures the intensity of X-rays reflected from a surface (or interference pattern) that is characteristic of the distance between interfaces. The thickness of the SAMs was consistent with fully extended alkyl chains with all-trans conformations and excellent agreement was observed between the two methods. 

Fig. 2.4 Low-energy electron diffraction (LEED). (a) Apparatus, showing how electrons reflected from a surface are detected by a fluorescent screen, (b) LEED pattern obtained from the surface of a tungsten oxide crystal. The bright spots show reflected electron beams. Measurement of their angles and Intensities gives information about the positions of atoms on the surface.

Used to determine thickness of an adsorbed film. A circular polarized beam of light is reflected from a surface, and the change in the polarization characteristics of the light gives information about the surface film. 

The specular reflectivity of neutrons, like the analogous light or X-ray reflectivity, from a surface or interface provides information about the neutron refractive index gradient or distribution in the surface region and in a direction orthogonal to the plane. This can often be simply related to a composition or concentration profile in the direction orthogonal to the surface, to provide directly information about adsorption and the structure of the adsorbed layer. 

Ellipsometry measures the orientation of polarized light undergoing oblique reflection from a sample surface. Linearly polarized light, when reflected from a surface, will become elliptically polarized, because of presence of the thin layer of the boundary surface between two media. Dependence between optical constants of a layer and parameters of elliptically polarized light can be found on basis of the Fresnel formulas described above. 

Different types of reflection from a surface (a) actual or irregular. ib) diffuse, and (c) specular or mirrorlike. 

An electron reflected from a surface carries diffraction information if it has experienced elastic scattering or information on the excitation of phonons, plasmons, and electronic or vibrational transitions as the result of inelastic events. The major effort in diffraction studies has concentrated on the use of low energies ( 200 eV) but reflection high-energy electron diffraction (RHEED 20—40keV) is suitable also for surface work (see ref. 2 for a description of pattern interpretation). RHEED... 

Figure 24. (A) Depiction of specular and first-order Bragg reflection from a surface. (B) Generation of an x-ray standing-wave field. (C) Movement of an x-ray standing-wave field in the — H direction upon advancing the angle of incidence across a Bragg reflection. (From Abruna, H. D., White J. H., et al., J. Phys. Chem. 92, 7045 (1988), with permission.)...

If a linearly polarized beam is reflected from a surface, one usually finds that the parallel and perpendicular components undergo different changes in amplitude and phase. Thus individual pairs of rays in the two beams are in phase upon incidence, but are out of phase upon reflection. This effect has interesting consequences, as shown in Figure... 

In external reflectance the incident radiation is focused on to the sample, and two forms of reflectance can occur, namely specular and diffuse. External reflectance measures the radiation reflected from a surface. The material must therefore be reflective, or be attached to a reflective backing. A particularly useful application of this technique is the study of surfaces. 

For a discussion of reflectance spectroscopy, two types of reflectance must be defined, specular and diffuse. Specular reflectance is simply mirrorlike reflectance from a surface and is sometimes called regular reflectance it has a well-defined reflectance angle. Diffuse reflectance is defined as reflected radiant energy that has been partially absorbed and partially scattered by a surface with no defined angle of reflectance. The diffuse reflectance technique is widely used today for industrial applications involving textiles, plastics, paints, dyestuffs, inks, paper, food, and building materials. In the area of basic research, diffuse reflectance spectroscopy has been used in studies of solid-solid reactions, of species absorbed on metal surfaces, of radiation transfer, and of slightly soluble species. 

Light is reflected from smooth surfaces following the law of reflection, the angle of incidence, 0, is equal to the angle of reflection, 6 (Figure 14.16). The amount of light reflected from a surface at normal incidence (i.e. perpendicular to the surface) is given by the coefficient of reflection, r. 

The ratio of the energy carried by a wave that is reflected from a surface to the energy of a wave incident on the surface. 

Spectral Reflectance - The ratio of energy reflected from a surface in a given waveband to the energy incident in that waveband. 

Layer thickness and polymer concentration is obtained directly by ellipsometry, that is, the change in elliptically polarized light after reflection from a surface covered by an adsorbed layer. The number of adsorbed segments is accessible via infrared spectroscopic studies as well as via calorimetric adsorption enthalpy measurements. 

The amount of light reflected from a surface of a material in air is determined by the refractive index of the reflecting medium. At normal incidence, the fraction, R, of light reflected (in medium 1) from the interface between two dielectric materials (1 and 2) is given by Fresnel s equation ... 

Ellipsometry [112, 113 Ellipsometry is one of the earliest optical technique to be applied to the study of adsorption processes [112, 113]. It involves the analysis of the phase change and the change in amplitude ratio of polarized light reflected from a surface. 

Collective name for a number of techniques dealing with the measurement and interpretation of the change in the polarization state of a polarized beam of radiation which is reflected from a surface. 

Ellipsometry is an optical technique that detects the change of the polarization state when light is reflected from a surface. For rather simple systems like transparent films on reflecting substrates, film thickness and refractive index can be determined with high accuracy. More complicated samples (e.g., multilayer structures or layers with a graded index of refraction on a reflective carrier) can be characterized with a sufficient set of independent experimental data obtained for multiple angles of incidence and/or multiple wavelengths (spectroscopic ellipsometry). With a liquid cell, ellipsometry can be performed also in aqueous environments. 

The incident radiation focused onto the sample may be directly reflected by the sample surface, giving rise to specular reflection, and it may also undergo multiple reflections at the sample, resulting in diffuse reflection. In external reflectance techniques, the radiation reflected from a surface is evaluated (Figure 8). 

The flame emissivity is presoibed as 0.9. This can be used without ambiguity for plane surfaces but, for finned surfaces, the thin flames between the fins will have an emissivity much lower than that value. The dominant source of radiation to the finned surfaces will therefore be the flames outside the fins radiation from flames within the fin cavity can be ignored. In all cases, appropriate geometric view factors should be used with the fin envelope radiation source, and reflected radiation should be taken into account. Care should be taken to avoid the inclusion of radiation reflected from a surface representing flames as this is a non-typical situation. 

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